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(11) | EP 1 052 067 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Fluid-operated tool |
| (57) A fluid-operated tool for tightening and loosening threaded connectors has a ratchet
unit including a ratchet (6) connectable with a threaded connector to be tightened
and loosened and provided with a plurality of teeth, and a pawl (9) engageable with,
and disengageable from, the teeth of the ratchet, drive means (1-4, 13) movable over
an advance stroke to turn the ratchet when the pawl engages the teeth of the ratchet
so as to turn a threaded connector connected with the ratchet for tightening or loosening,
and a retract stroke in which the pawl (9) is disengaged from the teeth of the ratchet,
and a unit for sensing when the pawl falls into engagement with a tooth of the ratchet
and in response reversing the drive from the retract stroke to the advance stroke. |
[0001] This invention relates to fluid operated tools, and more particularly to such fluid operated tools which have drive means and a ratchet-pawl mechanism including a ratchet connectable to a threaded connector to be tightened and loosened, for example a bolt, a nut, etc. and a pawl which is engageable with and disengageable from the teeth of the ratchet under the action of the drive means.
[0002] One known tool of the general type referred to above is disclosed in US-A-4,409,865. In this tool a lever mechanism has two drive pawls. While one drive pawl engages the ratchet during a forward stroke of the piston, the other pawl is tilted back so as to slip over the ratchet teeth and to engage the ratchet tooth on the retract stroke of the piston while at that time the first drive pawl is tilted back. Therefore the ratchet turns forward both during the advance stroke and the retract stroke of the piston.
[0003] The problem with this known tool is that during use of the tool to tighten or loosen a nut on a bolt, the nut is turned from tight to loose or from loose to tight. When the nut is being tightened and the turning resistance of the nut increases with each stroke, the flexing of the lever mechanism also increases. This in turn requires a built-in overstroke which can be 50% more than the actually calculated stroke. This means that, with a loose nut the pawl which moves backward to catch another tooth falls in way behind that tooth and thus has a free forward movement, when the piston next moves the other way, until the front of the pawl hits the ratchet tooth. This unnecessary free forward movement can be quite extensive when the nut is loose and there is turning resistance, but becomes quite minimal when high torque is being applied to the nut. This means that when the nut is loose, a good part of the piston stroke is used just to overcome the overstroke and have the pawl engage with the ratchet tooth. When the nut is tighter, on the other hand, the overstroke is absorbed by the material flex. Since the mechanism described in the above mentioned patent allows for a continuous turning of the ratchet, and thus the threaded connector which the ratchet engages, it is important to eliminate the overstroke when the nut is loose since, otherwise, the turning motion is interrupted each time the tool switches from an advance stroke to a retract stroke.
[0004] Accordingly, it is an object of the present invention to provide a fluid-operated tool which eliminates the disadvantages of the prior art.
[0005] In keeping with this object and with others which will become apparent hereinafter, there is provided, according to one aspect of the present invention, a fluid-operated tool for tightening and loosening threaded connectors comprising ratchet means including a ratchet connectable with a threaded connector to be tightened and loosened and provided with a plurality of teeth, and a pawl engageable with and disengageable from said teeth of said ratchet; and drive means movable over an advance stroke in which said pawl engages the teeth of said ratchet so as to turn the latter in a given direction so as to turn a threaded connector connected with said ratchet for tightening or loosening, and over a retract stroke in which the pawl is disengaged from the teeth of said ratchet; characterised in that said fluid-operated tool further comprises sensing means associated with said pawl for sensing when the pawl falls into engagement with a tooth of said ratchet and, in response, reversing said drive means from said retract stroke to said advance stroke.
[0006] When the fluid-operated tool is designed in accordance with the present invention, it eliminates the above mentioned disadvantages of the prior art and provides for highly advantageous results.
[0007] Preferably the fluid-operated tool has a second pawl which is also engageable the teeth of said ratchet and is arranged so that during the advance stroke of said drive means the second pawl slips over the teeth of said ratchet while during the retract stroke of said drive means the second pawl engages with the teeth of said ratchet and turns the latter in the said given direction, and second sensing means associated with said second pawl so as to sense when the latter falls into engagement with a tooth of said ratchet and, in response, reversing said drive means from said forward stroke to said retract stroke.
[0008] According to another aspect of the present invention there is provided a fluid operated tool which has ratchet means including a ratchet connectable with a threaded connector to be tightened and loosened and provided with a plurality of teeth, and at least one pawl engageable in and disengageable from the teeth of the ratchet, drive means connected with the ratchet means and movable over an advance stroke to turn the ratchet when the at least one pawl engages the teeth of the ratchet so as to turn a threaded connector connected with the ratchet for tightening or loosening, and a retract stroke in which the at least one pawl is disengaged from the teeth of the ratchet, and means for sensing when the at least one pawl falls into engagement with a tooth of the ratchet and in response reversing the drive means from the retract stroke to the advance stroke.
[0009] When the fluid-operated tool is designed in accordance with the present invention, rather than changing direction of the piston of the drive means when the piston is fully extended or retracted, as is common in conventional tools, the piston changes direction immediately when the corresponding pawl falls into engagement. This provides a much faster free and low torque tightening and loosening operation. Taking into consideration that the hydraulic power packs in hydraulically-operated tools have a relatively low oil flow, the use of sensing means to sense the respective pawl movement can easily speed up the operation by 50%, especially during low torque applications.
[0010] Embodiments of the invention will now be described, by way of example only, with specific reference to the accompanying drawing, in which:
Figure 1 is a view schematically showing a fluid-operated tool in accordance with the present invention for tightening and loosening of threaded connectors; and
Figure 2 is a section taken on the line II-II of Figure 1.
[0011] A fluid-operated tool in accordance with the present invention has a housing generally designated with reference numeral 1. The tool is provided with drive means which include a cylinder 2 formed in the housing 1 and a piston 3 reciprocatingly movable in the cylinder 2 and having a piston rod 4. The cylinder 2 communicates with a pump 5 which supplies a working fluid into, and withdraws the working fluid from, the cylinder 2, and for this purpose is provided with a valve 20.
[0012] The fluid-operated tool further has a ratchet-pawl mechanism which includes a ratchet 6 provided on its outer periphery with a plurality of teeth. The ratchet 6 is turnably supported between two support plates 7 fixed in the housing 1. It has an inner polygonal opening with which it can be fitted directly on an outer polygonal surface of a threaded connector, for example a nut, or on a central shaft 8 which can be connected with a socket engageable in turn with the threaded connector. The ratchet-pawl mechanism further has two pawls 9 and 10. Each pawl has a front end provided with a tooth and a rear end, the rear ends of the pawls 9 and 10 being pivotably connected by pivot pins 11 and 12, respectively, to a drive plate 13. The drive plate 13 is itself pivotably connected to the support plate 7 by a pivot pin 14. The free end of the piston rod 4 of the drive means is pivotably connected to the drive plate 13 by a pivot pin 15.
[0013] During the operation of the fluid-operated tool, the piston 3, under the action of the working fluid supplied by the pump 5 into the cylinder 2, is displaced to the left, as viewed in Figure 1, (the forward stroke), the drive plate 13 is turned in counter clockwise direction and the pawl 9 engaging between the teeth of the ratchet 6 is displaced so as to turn the ratchet 6 and therefore a threaded connector engaged by it also in counter clockwise direction. During the advance stroke the pawl 10 just slips over the teeth of the ratchet 6. Then the piston 3, under the action of the working fluid, is moved to the right, as viewed in Figure 1, (the retract stroke), and the drive plate 13 is turned in clockwise direction, the pawl 10 engages between the teeth of the ratchet 6 and is displaced so as to turn the ratchet 6, and therefore a threaded connector engaged by the ratchet also, in counter clockwise direction. At that time the pawl 9 just slips over the teeth of the ratchet. Therefore the threaded connector engaged by the ratchet 6 turns in the same direction both during the advance stroke and the retract stroke.
[0014] In accordance with the present invention the pawls 9 and 10 are provided with sensing means 16 and 17, respectively. Each of the sensing means 16 or 17 is formed so that it senses when the corresponding pawl 9 or 10 falls into engagement with the tooth of the ratchet 6 and sends a signal for reversing the stroke of the drive means, for example to the valve 20 through control lines 21 and 22. In particular, when the sensing means 16 of the pawl 9 senses that the pawl 9 falls into engagement with the tooth of the ratchet 6, it sends a signal to the valve 20 of the pump 5, to act on the working fluid so as to switch from the retract stroke of the piston 3 to the advance stroke. The sensing means 17 of the pawl 10 sense when the pawl 10 falls into engagement with the tooth of the ratchet 6 and sends a signal to the valve 20 of the pump 5 to provide the action of the working fluid so as to switch from the advance stroke of the piston 3 to the retract stroke. As a result, the piston 3 changes its direction not when it is completely extended or retracted, but instead when the corresponding pawl 9, 10 falls into engagement with the teeth of the ratchet 6.
[0015] Each of the sensing means 16, 17 can be formed for example as shown in Figure 2. The sensing means can include, for example, a Hall effect sensor fixed to the support plate 7 and a magnet 19 fixed to a corresponding pawl 9 or 10. When the magnet 19 reaches the Hall effect sensor 18, the latter sends a signal to the valve 20 of the pump 5. It is to be understood that the positions of the Hall effect sensor 18 and the magnet 19 are selected so as to sense a desired degree of engagement of the corresponding pawl with the teeth of the ratchet.
[0016] While Figure 1 shows the fluid-operated tool with two drive pawls, such as for example disclosed in US-A-4,409,865, it is to be understood that the present invention is applicable to fluid-operated tools provided with a single pawl, such as shown for example in US-A-4,201,099 and US-A-5,005,447. Once the pawl falls into the ratchet tooth after ratcheting backwards, an immediate forward movement saves a lot of time as well.
1. A fluid-operated tool for tightening and loosening threaded connectors, comprising
ratchet means including a ratchet (6) connectable with a threaded connector to be
tightened and loosened and provided with a plurality of teeth, and a pawl (9) engageable
with and disengageable from the teeth of said ratchet (6); and drive means (2-4, 13)
movable over an advance stroke in which said pawl (9) engages the teeth of said ratchet
(6) so as to turn the latter in a given direction so as to turn a threaded connector
connected with said ratchet for tightening or loosening, and over a retract stroke
in which the pawl is disengaged from the teeth of said ratchet; characterised in that said fluid-operated tool further comprises sensing means (16, 19) associated with
said pawl for sensing when the pawl (9) falls into engagement with a tooth of said
ratchet and, in response, reversing said drive means from said retract stroke to said
advance stroke.
2. A fluid-operated tool according to claim 1, characterised in that the tool further
comprises a second pawl (10) which is also engageable the said teeth of said ratchet
(6) and is arranged so that during the advance stroke of said drive means the second
pawl (10) slips over the teeth of said ratchet while during the retract stroke of
said drive means the second pawl engages with the teeth of said ratchet and turns
the latter in the said given direction, and second sensing means (17, 19) associated
with said second pawl (10) so as to sense when the latter falls into engagement with
a tooth of said ratchet and, in response, reversing said drive means from said forward
stroke to said retract stroke.
3. A fluid-operated tool according to claim 1 or 2, characterised in that the tool further
comprises a support member (7) relative to which the or each pawl is movable, and
in that the or each sensing means includes a first sensing element (16, 17) arranged
on the, or the associated, pawl and a second sensing element (19) arranged on said
support member (7), so that when the or each pawl falls into engagement with a tooth
of said ratchet, the sensing elements interact with one another so as to produce a
signal for reversing the stroke of said drive means.
4. A fluid-operated tool according to claim 3, characterised in that, for the or each
sensing means, one of said sensing elements is a magnet (19) and the other of said
sensing elements is a Hall sensor (16, 17).
5. A fluid-operated tool according to any one of the preceding claims, characterised
in that said drive means comprises cylinder-piston means (2-4).